The present invention relates generally to blackboard or wall erasers, and more particularly to an apparatus providing guided manual cleaning action for removing chalk or other marks from selected portions of a blackboard or like erasable and reusable writing surface on a wall.
U.S. Pat. Nos. 2,167,296 (Farmer); 3,858,265 (Schlick) and 3,731,335 (Chrisp) show previously proposed blackboard cleaning devices. Each of these proposed devices provides a motorized mechanism, and has an eraser or sponge and an associated mount extending vertically to cover the entire height of the blackboard, the erasers or sponges being continuously engaged with the surface of the board. Thus, each device is designed to erase or clean an entire board in one pass or sweep of the eraser over the entire surface of the board, controlled entirely by a motorized drive. None of the proposed devices can erase a selected portion of the board while leaving other portions unerased, such as, for example, the bottom half or a single quadrant.
U.S. Pat. No. 3,163,943 (Bell) shows a manually operated mechanical blackboard eraser having means for selectively disengaging the eraser from the board to leave a portion of the board unerased. However, the eraser and its associated mount again extend over the entire height of the board; hence a full-height vertical section of the board must be left uncleaned to save what is written on any part of that section.
Since each of the prior devices mentioned above has an erasing or cleaning member of more or less complex structure extending for the full height of the blackboard, it is necessary to custom-make (or at least custom-fit) the erasing/cleaning member for a particular blackboard height, and the custom-made erasing/cleaning member cannot be used with a blackboard of a different height. Both the inherent cost of the large erasing/cleaning member, and the inability to produce such members in a single size to fit all blackboards, add to the expense of manufacture of the prior devices.
In addition, since none of the erasers and sponges of the abovedescribed prior devices is readily detachable from its associated mount, cleaning and replacement of the eraser or sponge is difficult.